Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$216.43	12.464%	$243.4058	$243.41	$243.40	$243.40
Purchase #2	$96.32	4.147%	$100.3144	$100.31	$100.30	$100.30
Purchase #3	$144.68	4.151%	$150.6857	$150.69	$150.70	$150.70
Purchase #4	$109.90	11.153%	$122.1571	$122.16	$122.15	$122.20
Purchase #5	$109.68	10.314%	$120.9924	$120.99	$121.00	$121.00
Purchase #6	$145.76	3.685%	$151.1313	$151.13	$151.15	$151.10
Purchase #7	$86.30	4.206%	$89.9298	$89.93	$89.95	$89.90
7 purchase totals =	$909.07		$978.6165	$978.62	$978.65	$978.60